Process of preparing stable triglycerides of fat forming acids



Feb. 23, 1965 R. o. FEUGE ETAL 3,170,799

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INVENTORS REUBEN O. FEUGE WERNER LANDMANN ATTORNEY United States Patent M 3,170,799 PROCESS OF PREPARING STABLE TRIGLYCER- IDES 0F FAT FORMING ACIDS Reuben O. Feuge and Werner Landmann, New Orleans,

La., assignors to the United States of America as represented by the Secretary of Agriculture Filed Nov. 28, 1961, Ser. No. 155,514 6 Claims. (Cl. 99-118) (Granted under Title 35, US. Code (1952), see. 266) A nonexclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to a process for producing stable fatty triglycerides and more particularly to a process for producing the thermodynamically stable polymorphic form of solid fatty triglycerides.

More particularly, this invention relates to a process whereby fats in thermodynamically unstable form, whether alone or in a mixture with nonfat constituents, are transformed to the thermodynamically stable form. The transformation, which is the subject of this invention, is brought about by subjecting the fatty material to mechanical working to a degree sufiicient to force the polymorphic transformation.

In order that the invention may be better understood, reference is made to the following description and to the accompanying drawings in which:

FIGURE 1 represents the diffraction pattern of an unworked sample of cocoa butter;

FIGURE 2 represents the diffraction pattern of a worked sample of cocoa butter; and

FIGURE 3 represents the diffraction pattern of cocoa butter before melting.

Almost invariably the solid triglycerides of the edible, fat-forming acids are able to exist in two or more polymorphic forms. Polymorphic transformations are to be regarded as true phase changes, comparable to melting or solidification, as they involve reconstruction of the crystal lattice and are accompanied by discontinuities in the heat content, the specific volume, and certain other properties of the triglycerides or fat. Usually the transformations encountered in the ordinary melting and solidification of triglycerides of edible, fat-forming acids are three or four in number. The transformations in ordinary melting and solidification are nearly always monotropic in nature; that is, the transformations are seldom reversible and nearly always occur in one direction, from the lowest to the highest melting polymorphic form.

Invariably melting and resolidification are required to convert a triglyceride of edible, fat-forming acids from the thermodynamically stable polymorphic form to an unstable form. In the transition from liquid to progressively higher melting and more stable crystal forms, the crystal lattice becomes more highly ordered and more closely packed, and the density and heat of fusion increase.

The state of the space lattice in the case of crystalline triglycerides may conveniently be determined from X-ray ditfraction patterns. Among physical scientists versed in the polymorphism of triglycerides certain interplanar distances calculated from the strong bands of the diffraction pattern are indicative of a given polymorphic form. For triglycerides in general, three distinctive forms and their associated short spacings, in Angstroms, are as follows:

Beta 4.6 (strongest), 3.85, 3.7. Beta prime 4.2 (usually strongest), 3.8. Alpha 4.15 (strong), others very weak.

Some triglycerides, like the 2-oleo disaturated triglyc- 3,170,799 Patented Feb. 23, 1965 erides, are stable in the beta form, while others, like the f1-oleo disaturated triglycerides are stable in the beta prime orm.

I The degree to which a triglyceride or a fat has been stabilized also can be determined from its melting point. The highest melting point is obtained when the triglyceride or fat is in the thermodynamically stable form.

The hardness of a triglyceride or fat, as measured by a modification of the Brinell test for metals, also is indicative of the degree of stabilization. As the triglyceride or fat changes into higher-melting polymorphs the hardness increases.

The polymorphic state of solid or semisolid fats or of products containing such fats is of considerable practical importance. In the chocolate industry much time and expense are involved in ensuring that the semisolid chocolate contains the proper amount of stable seed crystals just prior to the molding and enrobing operations. To obtain an adequate supply of properly tempered chocolate, a large amount of chocolate is carefully heated in a large kettle, the temperature is reduced to just the right level, and shavings of solid chocolate in which the cocoa fat is in the thermodynamically stable form are introduced. Prolonged mixing is required to properly disperse these seed crystals. This so-called tempered chocolate is used in subsequent molding and enrobing operations.

If the above-described procedure has been carried out properly, then the surface of the finished pieces of chocolate will be hard and glossy after passing through the cooling tunnel and will remain in this condition on storage at room temperature. If the procedure has not been carried .out properly, the pieces of chocolate will become soft and sticky on coining to room temperature, and their appearance will be ruined. Also, failure of the cocoa fat in the chocolate to be converted quickly to the most stable polymorphic form can result in the subsequent development of fat bloom, which usually means that the candy retailer will return the candy to the manufactureras unsalable.

Candies containing certain cocoa butter-like fats instead of cocoa fat must also be manufactured so as to ensure the fat being in the most stable polymorphic form.

Numerous other examples can be cited in which it is important that the crystals of a solid or. semisolid fat be in the most stable polymorphic form.

In the manufacture of compound-type shortenings, a" more satisfactory product could be produced if the solid phase could be converted initially to the most stable form. In such shortenings a highly hydrogenated oil is melted, mixed with a liquid oil, and the mixture is cooled to room temperature to produce a semisolid mass. Subsequently,

slow changes in the polymorphic form of the fat crystals accompanied by crystal growth impairs the texture, butit does increase the plastic range by raising the melting point of the crystals. sirable. If it were possible to immediately transform the minute fat crystals in a quickly chilled mass to the most stable form, subsequent changes would be minimized, and the longer plastic range would be obtained immediately.

Heretofore, it has been the practice to convert fats to their highest-melting, most stable polymorphic form by' one or a combination of three procedures; (1) seeding The increased plastic range is devention contemplates subjecting certain unstable polymorphs of triglycerides of fat-forming fatty acids to a mechanical process of extrusion, compression, mastication, kneading, milling, or other treatment which subjects a solid working material to physically distortive forces. It is generally preferred to use a working process such as extrusion which facilitates control of the temperature of the. material beingworked. The working process may be carried out so as to effect substantially complete conversion' to the stable form or to effect only a partial conversion. In the latter instance the unconverted material may be subsequently converted by holding the entire mass for a short time at a temperature just below its melting point or by partially melting the mass and then resolidifying it; that is, the crystals converted by mechanical working are made to serve as seed crystals.

The type of mechanical working required to practice the present invention is entirely different from that currently used in the manufacture of shortenings and confections. In the Votator commonly used in. the manufacture of shortenings and in the enrober commonly used in the manufacture of chocolate confections masses containing semisolid fats are worked to break up clumps of fat crystals and produce a smooth textured mass. It is common knowledge that the Votator and other mechanical devices currently in use in the manufacture of solid and semisolid fats do not convert a product like highly hydrogenated cottonseed oil into the most stable polymorphic form. Such products, as well as commercial shontenings, customarily are tempered prior to being used. Such tempering consists of holding the products at a predetermined temperature for a certain minimum time. The enrober used in the chocolate industry does not con- Vert the crystals of cocoa fat in the semisolid chocolate to the most stable polymorphic forms even though the chocolate mass is worked continuously by a mechanical P p- The pressures and amount of work per unit mass required to practice the present invention are of a different order of magnitude from' those currently used in the manufacture and use of solid and semisolid fats. For example, to effectively deform and work the individual crystals of a mass of solid fat by extrusion, we found it necessary'to use a force of about 1,000 pounds per square inch and to push the solid fat several times through a cluster of three orifices, each orifice measuring 0.0135 inch in diameter.

The mechanical working required to practice the present invention is not of the type which occurs when a liquid fat is cooled and crystallized while being stirred. Such stirringmay enhance crystallization from the liquid phase into a higher melting polymorphic form but has no effect on converting difficult-to-tr-ansform fats into the highest melting polymorphic form. Such stirring does not work or deform individual crystals to the extent that a solidto-solid transformation occurs.

In the practice of the present invention the efficiency of mechanical working in effecting a phase transformation from an unstable solid form to the stable polymorph is a function of temperature; the efiiciency of the process increases as. the temperature of the material being worked rises up to just short of the melting point. A preferred. embodiment of the present invention comprises mechanically working an unstable fatty triglyceride polymorph. at a. temperature approaching its melting point since such an operation affords a maximum conversion with aminimum of 'working.

While the present invention may be practiced with any of the triglycerides of fat fQrming acids or of mixtures of such triglycerides, there may be no practical advantage tousing the invention in allinstances. A brief presentation concerning-thenature of triglycerides and their polymorphism will illustrate this point.

A great variety of triglycerides are found in natural fats or can be derivedfrom-such natural fats. This great variety results from the nature of a molecule of tniglyceride, which consists of three fatty acid groups attached to a glycerol moiety. The types of fatty acids and their spatial arrangement in the triglyceride molecule determine the properties of the triglyceride molecule. Thus with a mixture of fatty acids consisting of myristic, palmitic, stearic, oleic, linolezic, and linolenic it is possible to prepare 196 triglycerides which differ from each other in physical and chemical properties.

Among this variety of triglycerides, the nature of the polymorphic transformations, the conditions under which they proceed, and their rates vary widely. Some transform .so readily that their polymorphism presents no problem in utilization, the highest melting forms appearing normally a few minutes after the triglyceride is solidified. Other triglycerides, which are the ones with which this invention is concerned, present marked problems in utilization. Such triglycerides may require days and even weeks of tempering just below their melting points in order to effect transformation to the highest melting or most stable form. 2-oleodistearin and 2-oleopalmitosteanin, which are the main components in cocoa butter and are important components of some other confectionery fats, are among the triglycerides which are difficult to temper to the most stable polymorphic form. Mixtures of these triglycerides, which are found in cocoa butter and certain other confectionery fats, are even more difficult to temper to the stable polymorphs than are the pure triglycerides. Completely hydrogenated cottonseed oil and completely hydrogenated tallow are other fat products which have been found difficult to temper to the stable polymorphic form.

From a practical standpoint the invention would not be practiced with fat mixtures containing a very large variety of triglycerides. Such mixtures almost invariably contain triglycerides which readily transform to the most stable form. Each of the other triglycerides is present in such small proportions, and its crystals are so admixed with other types of crystals that transformation to the most stable form does not greatly affect the properties of the whole mass. A relatively homogenous solid phase cannot be attained. For the practice of this invention about 20% of the triglycerides in a mixture should be of one type or very closely related types. 2-oleodistearin and 2-ole0palmitostearin are considered to be very closely related types because their physical structures and polymorphic behaviors, and melting points are quite similar.

As the chain lengths of the fatty acid groups in a triglyceride decrease, the rate at which polymorphic trans formations occur increase. When the average chain length is less than that about 12 carbon atoms, the rate of transformation generally is sufficiently rapid so that polymorphism does not present a difficult problem in the utilization of such triglycerides. As a practice example, candy coating compositions made with palm kernel stearine present no particular problems in tempering during the manufacture of candies, nor do the finished candies exhibit any marked tendency to bloom. The term bloom refers here to fat bloom, which is the appearance of whitish spots on the surface of the candy caused by recrystallization of the fat in the coating composition.

Also, our invention has relatively little value in the utilization of triglycerides of short-chain fatty acids because such triglycerides tend to be low-melting and usual- 1y contain few solids at room temperature. Thus, coconut oil, which is composed of mixed triglycerides of caprylic, capric, lauric, myristic, palmitic, and oleic acids, usually melts between 24 and 27 C. and is semisolid at somewhat lower temperatures.

An unexpected feature of the present invention is that it can be practiced when the fat crystals are mixed with liquid fats or with nonfat solids. Thus, the solid cocoa fat in cooking chocolate, which contains about 46% of non fat solids, could be transformed to the stable polymorph by mechanical working of the entiremixture. Likewise,

the solid cocoa fat in milk chocolate could be converted by mechanical working at a temperature at which some of the milk fat in the milk chocolate was liquid.

The following examples will serve as illustrations of a preferred embodiment of the present invention, but it is to be understood that the invention is not limited thereto.

Commercial cocoa butter was melted and heated to 70 C. to destroy all crystal nuclei. A thin layer of the melt was poured into a beaker, and the contents were cooled rapidly with Dry Ice. The breaker was taken into a Walkin cooler kept at 4 C., and a portion of the cocoa butter was removed and extruded ten times through a sodium press. Suflicient time was allowed between extrusions so that the temperature of the extruded cocoa butter always remained below about C. and no visible melting occurred. On about the fifth or sixth extrusion the extruded fat became much harder. A total of ten extrusions was made. Then the worked and unworked cocoa butter were forced into separate molds and X-ray diffraction pat-. terns were obtained.

The X-ray diffraction patterns were obtained with an X-ray machine employing an argon-filled proportional counter tube. The X-ray tube had a copper target and a nickel filter and was operated at 45 kv. and ma. A onedegree slit was used in collimating the two-theta angle between 10 and degrees. FIGURES l and 2 represent the patterns of the unworked and worked samples of cocoa butter, respectively. FIGURE 3 represents the pattern of the original cocoa butter before melting and is typical of cocoa butter in which the components are in the highest melting or thermodynamically stable polymorphic form. The peaks at 19.3 represent a short spacing of 4.6 Angstroms in the crystal lattice. A strong line representing this spacing indicates the presence of the beta polymorphic form, which is the stable polymorphic form of the triglycerides of cocoa butter. As is evident from FIGURE 1, the quickly solidified and unworked sample of cocoa butter does not exhibit in its pattern a strong line at 4.6 Angstroms, which indicates the absence of the stable beta form. FIGURES 2 and 3 do exhibit such lines. Hence, FIGURE 2 is proof of the fact that working of the solid, unstable crystals of cocoa butter transforms them into crystals of the stable polymorphic form.

A cocoa butter-like fat, which consisted essentially of oleodisaturated glycerides of palmitic and stearic acids, was put through the same treatment just described for cocoa butter.

To obtain this cocoa butter-like fat, three parts of almost completely hydrogenated cottonseed oil and one part of olive oil were interesterified in the presence of sodium methoxide as catalyst. One part of the purified reaction product was dissolved in four parts by weight of acetone and the solution was cooled stepwise to 33 F. The fraction separating out of solution between 63 F. and 33 F. was collected and after removal of residual acetone was dissolved in petroleum ether (1 to 1 by weight). The petroleum ether solution was cooled to room temperature and the solids which formed were removed by filtration. The filtrate was collected and the petroleum ether was removed to obtain the cocoa butterlike fat, which melted over about the same temperature range as does cocoa butter.

A sample of the cocoa butter-like fat was melted and quickly solidified by the procedure described above for cocoa butter, and a portion of the quickly chilled, solid sample was worked below its melting point, again as described for cocoa butter. The X-ray diffraction pattern of the worked sample did not resemble that of the quickly chilled but unworked sample; instead, the pattern resembled that of an aged and well-tempered sample of the same cocoa butter-like fat. None of the patterns of the cocoa butter-like fat resembled those of cocoa butter partly because most of the components of the cocoa butter-like fat were thermodynamically stable in the beta prime polymorphic form rather than the beta form.

The applicability of the invention was demonstrated with still another type of fat. A commercially available sample of almost completely hydrogenated cottonseed oil (iodine value, 2.0) was put into a beaker in such an amount that after melting a layer about one centimeter deep was produced. The melted sample was heated to C. to destroy all seed crystals. Then the beaker was chilled with ice to quickly solidify the sample. The sample and beaker were warmed to room temperature, about 25 C., and a portion of the sample was removed and extruded ten times through a sodium press. X-ray diffraction patterns of the worked and unworked portions of the sample were obtained. Also, an X-ray diffraction pattern was obtained for a portion of the original, almost completely hydrogenated cottonseed oil which had been kept in the solid state for many months prior to the time the X-ray diffraction pattern was obtained and which had been stored for over 12 days at a temperature just below its melting point immediately before the pattern was obtained. The pattern of that portion of the sample which was solidified quickly and then worked while in the solid state did not closely resemble the pattern of the portion of the sample which was quickly chilled but not worked. The pattern of the worked portion of the quickly chilled sample exhibited the same diffraction lines found with the sample which had been aged for several months in the solid state and then tempered for over 12 days by holding it at a temperature just below its melting point.

The invention can be practiced with solid fats admixed with nonfats, which fact makes the invention particularly useful in the commercial processing and handling of chocolate liquor or unsweetened cooking chocolate. This product, which consists of the roasted and finely ground kernels of the cocoa bean and which contains about 54% cocoa fat, is an important ingredient in the manufacture of chocolate confections.

Chocolate liquor was melted and heated to 67 C. to destroy all of the crystals of cocoa fat. The chocolate liquor then was quickly solidified by cooling the beaker containing it in an ice bath. The beaker and its contents were taken into a walkin cooler kept at 4 C., and a portion or" the solidified chocolate liquor was removed from the beaker and extruded ten times through a small orifice.

When the worked and unworked portions were warmed to room temperature (25 C.), partial melting of the unworked portion occurred; but the worked portion did not melt. Both portions were heated to 34 C., at which temperature most of the solid fat melted. Both portions were kept at this temperature for one-half hour, then poured into molds and solidified by storing in a refrigerator for one-half hour at 5 C. The temperature of the samples then was allowed to increase gradually and hardness tests were made.

The following hardness indices were obtained:

Hardness index X 10 Temp, 0.

Worked Sample Unworked Sample possessed a good gloss and good contraction and could be demolded readily; whereas those made with the unworked chocolate liquor possessed poor gloss and poor contraction and could not be demolded. The bars made from the worked chocolate liquor behaved in every respect like bars made from chocolate liquor which had been seeded adequately with crystals of the stable polymorphic form of cocoa butter.

Tests similar to those carried out with chocolate liquor were carried out with milk chocolate. With the latter product the temperature at which the mechanical working of the solid cocoa fat was carried out was such that some of the milk fat remained in the liquid phase. The results obtained with the milk chocolate were similar to those obtained with the chocolate liquor.

To one skilled in the art it is obvious that several forms of this invention might be practiced in the manufacture of chocolate confections and other products containing solid or semisolid fats. For example, in the manufacture of chocolate a mass containing partially solidified fat might be worked to convert only a portion of the solid fat into seed crystals of the stable polymorphic form; or as an alternative, the chocolate mixture flowing to the molding or enrobing machinery might be divided into two streams in one of which the fat is soldified and worked, and then the streams could be recombined.

We claim:

1. A process for producing the thermodynamically stable polymorphic form of solid triglyceride mixtures wherein at least 20 weight percent consists of closely related triglyceride types and wherein the triglyceride component fatty acids contain at least 12 carbon atoms, said process consisting of forcing the said triglyceride mixture at a temperature below the melting point and at a pressure of at least 1000 pounds per square inch through an orifice about .01 inch in diameter.

2. The process of claim 1 wherein the triglyceride mixture in unstable crystalline form is a confectionery coating composition containing cocoa butter.

3. The process of claim 1 wherein the triglyceride mixture in unstable crystalline form contains at least about 2 0% by weight of a single triglyceride type.

4. The process of claim 1 wherein the triglyceride mixture in unstable crystalline form is predominantly 2-oleopalmitostearin and 2-oleodistearin, the 2-oleopalmitostearin being present in an amount by weight at least about double that of Z-Oleodistearin.

5. The process of claim 1 wherein the triglyceride mixture in unstable crystalline form is cocoa butter.

6. The process of claim 1 wherein the triglyceride mixture in unstable crystalline form is hydrogenated cottonseed oil.

References Cited by the Examiner UNITED STATES PATENTS 2,234,931 3/41 Newton et al. 99118 2,384,077 9/45 Crosley et al 99-23 2,521,243 9/50 Mitchell 99118 X OTHER REFERENCES Meara, J. Chem. Soc., 1949, pp. 2154 to 2157. Chapman et al.: J. Chem. Soc., 1957, pp. 1502 to 1509.

A. LOUIS MONACELL, Primary Examiner. TOBIAS E. LEVON, Examiner. 

1. A PROCESS FOR PRODUCING THE THERMODYNAMICALLY STABLE POLYMORPHIC FORM OF SOLID TRIGLYCERIDE MIXTURES WHEREIN AT LEAST 20 WEIGHT PERCENT CONSISTS OF CLOSELY RELATED TRIGLYCERIDE TYPES AND WHEREIN THE TRIGLYCERIDE COMPONENT FATTY ACIDS CONTAIN AT LEAT 12 CARBON ATOMS, SAID PROCESS CONSISTING OF FORCING THE SAID TRIGLYCERIDE MIXTURE AT A TEMPERATURE BELOW THE MELTING POINT AND AT A PRESSURE OF AT LEAST 1000 POUNDS PER SQUARE INCH THROUGH AN ORIFICE ABOUT .01 INCH IN DIAMETER. 